Cancer is a disease in which cells grow in an abnormal way. Normally, the cells divide in a controlled manner to replace old or damaged cells. If cells keep dividing when new cells are not needed, a mass of tissue called a tumor forms.
A tumor can be benign or malignant. A benign tumor is not cancer and will not spread to other parts of the body. A malignant tumor is cancer. Cancer cells invade and damage tissue around them. The cancer cells can also enter the lymph and blood streams, spreading to other parts of the body. Breast cancer is the development of malignant cells in the breast tissue.
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Breast cancer is the most common form of cancer found in women, though lung cancer claims far more lives. Although the majority of breast cancer cases occur in women, it occurs in men as well. This fact sheet focuses on breast cancer in women.
A breast consists of glandular tissue called lobes. These lobes are divided into lobules, which can produce milk. Milk is carried from the lobules to the nipple by small ducts. All of this is surrounded by fatty and connective tissue, as well as blood and lymph vessels.
Breast cancer can start anywhere in the breast tissue, but the most common places are in the glandular tissue like ducts and lobules. The cancer cells may eventually form a tumor, or invade nearby tissue, such as the chest wall or lymph glands.
Lymph vessels delivers fluid from around the tissue, back into the blood stream. When it detects foreign matter, like bacteria or viruses, lymph nodes will help create blood cells to fight the infection. The lymph can also carry cancer cells away from the original tumor site and allow cancer to travel to other areas of the lymph or body. The lymph vessels around the breast lead to lymph nodes under the arm, above the collarbone, and in the chest. Cancer that has spread to other areas of the body is called metastatic cancer. The most common sites for metastatic breast cancer are the bones, lung, brain, and liver.
Breast cancer can develop in different ways and may affect different parts of the breast. The location of cancer will affect the progression of cancer and the treatment.
Breast cancer can also be classified by its invasiveness.
LCIS does not warrant treatment by surgery or radiation therapy. Your doctor will monitor the LCIS with regular check-ups and tests to see if there is any further development.
Paget's disease is cancer of the areola and nipple. It is very rare, occurring in less than 1% of all breast cancers. Although Paget's does not arise from glandular tissue in the breast, it can be associated with both in situ and invasive breast cancers. Generally, women who develop this type of cancer have a history of nipple crusting, scaling, itching, or inflammation.
Breast cancer. American Cancer Society website. Available at: http://www.cancer.org/acs/groups/cid/documents/webcontent/003090-pdf.pdf. Accessed October 21, 2015.
Breast cancer. Merck Manual Professional Version website. Available at: http://www.merckmanuals.com/professional/gynecology-and-obstetrics/breast-disorders/breast-cancer. Updated September 2013. Accessed October 21, 2015.
Breast cancer in women. EBSCO DynaMed website. Available at: http://www.ebscohost.com/dynamed. Updated June 18, 2015. Accessed October 21, 2015.
General information about breast cancer. National Cancer Institute website. Available at: http://www.cancer.gov/types/breast/patient/breast-treatment-pdq. Updated August 13, 2015. Accessed October 21, 2015.
Last reviewed December 2014 by Mohei Abouzied, MD Last Updated: 10/21/2015